Sea angels (clade Gymnosomata) are a large group of extremely small, swimming sea slugs, not to be confused with Hydrozoans (Jellies and other similar creatures), classified into six different families. They are pelagic opisthobranchs in the clade Gymnosomata within the larger clade Heterobranchia. Sea angels were previously referred to as a type of pteropod.
Sea angels are also sometimes known as "cliones" but this is potentially misleading because the family Clionidae is just one of the families within this clade.
Recent molecular data suggest the Gymnosomata form a sister group to the Thecosomata (other planktonic, weakly or nonmineralized gastropods), but this long-standing hypothesis has also had some recent detractors.
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